Flow cytometry of bacteria: glimpses from the past with a view to the future

Surface PEGylation of ionophore-based microspheres enables determination of serum sodium and potassium ion concentration under flow cytometry

We present here an ionophore-based ion-selective optode (ISO) platform to detect potassium and sodium concentrations in serum through flow cytometry. The ion-selective microsensors were based on polyethylene glycol (PEG)-modified polystyrene (PS) microspheres (PEG-PS). Ratiometric response curves were observed using peak channel fluorescence intensities for K⁺ (10^-6 M to 0.1 M) and Na⁺ (10^-4 M to 0.2 M) with sufficient selectivity for clinical diagnosis. Due to the matrix effect, proteins such as albumin and immunoglobulin caused an obvious increase in response for serum sample determination. To solve this problem, 4-arm PEG chains were covalently attached onto the surface of PS microspheres through a two-step reaction, which improved the stability and combated pollution of microspheres. As a preliminary application, potassium and sodium concentrations in human serums were successfully determined by the PEG-PS microsensors through flow cytometry.

Flow Cytometric Analysis of Oxidative Stress in Escherichia coli B Strains Deficient in Genes of the Antioxidant Defence

The detection of reactive oxygen species (ROS) and the analysis of oxidative stress are frequent applications of functional flow cytometry. Identifying and quantifying the ROS species generated during oxidative stress are crucial steps for the investigation of molecular mechanisms underlying stress responses. Currently, there is a wide availability of fluorogenic substrates for such purposes, but limitations in their specificity and sensitivity may affect the accuracy of the analysis. The aim of our work was to validate a new experimental model based in different strains of Escherichia coli B deficient in key genes for antioxidant defense, namely oxyR, sodA and sodB. We applied this model to systematically assess issues of specificity in fluorescent probes and the involvement of different ROS in a bacterial model of oxidative stress, as the probes can react with a variety of oxidants and free radical species. Our results confirm the higher sensitivity and specificity of the fluorescent probe mitochondrial peroxy yellow 1 (MitoPY1) for the detection of H₂O₂, and its very low capacity for organic hydroperoxides, thus extending MitoPY1's specificity for H₂O₂ in mammalian cells to a bacterial model. On the contrary, the fluorescent probe 2',7'-dichlorodihydrofluorescein diacetate (H₂DCF-DA) is more sensitive to organic peroxides than to H₂O₂, confirming the lack of selectivity of H₂DCF-DA to H₂O₂. Treatment with organic peroxides and H₂O₂ suggests a superoxide-independent oxidation of the fluorescent probe Hydroethidine (HE). We found a positive correlation between the lipophilicity of the peroxides and their toxicity to E. coli, suggesting greater quantitative importance of the peroxidative effects on the bacterial membrane and/or greater efficiency of the protection systems against the intracellular effects of H₂O₂ than against the membrane oxidative stress induced by organic peroxides. Altogether, our results may aid in preventing or minimizing experimental errors and providing recommendations for the proper design of cytometric studies of oxidative stress, in accordance with current recommendations and guidelines.

Quantitative assessment of bacterial growth phase utilizing flow cytometry

Flow cytometry is currently underutilized for bacterial phenotyping and standard microbiological techniques do not provide phenotypic information about the state of the bacterial disease. Pseudomonas aeruginosa is a human pathogen of increased importance in public health due to both the ability to cause chronic diseases and the prevalence of functionally different subsets that can be difficult to treat and diagnose. In the present study, we used flow cytometry to analyze the growth phase of P. aeruginosa. A simple method for single cell quantitative detection of bacterial biofilm and planktonic cells was established with a combination of membrane permeable (SYTO 60) and impermeable (TOTO-1) dyes plus the addition of polystyrene counting beads. The specificity of the dye combination for biofilm detection was determined by comparison with impaired biofilm forming strains of P. aeruginosa LasI/RhlI-/- and ∆PfPhage. Results suggest that flow cytometric bacterial phenotyping serves as an expandable platform that may be useful for enumeration of population level variation in P. aeruginosa studies.

Rapid and Sensitive Quantification of Anammox Bacteria by Flow Cytometric Analysis Based on Catalyzed Reporter Deposition Fluorescence In Situ Hybridization

The quantification of anammox bacteria is crucial to manipulation and management of anammox biosystems. In this study, we proposed a protocol specifically optimized for quantification of anammox bacteria abundance in anammox sludge samples using catalyzed reporter deposition-fluorescence in situ hybridization (CARD-FISH) and flow cytometry (FCM) in combination (Flow-CARD-FISH). We optimized the pretreatment procedures for FCM-compatibility, as well as the permeabilization, hybridization and staining protocols of the CARD-FISH. The developed method was compared with other methods for specific bacteria quantification (standard FISH, 16S rRNA sequencing and quantitative polymerase chain reaction). Anammox sludge samples could be disaggregated effectively by sonication (specific energy of 90 kJ·L^-1 with MLVSS of 3-5 g·L^-1) with the mixed ionic and nonionic dispersants Triton X-100 (5%) and sodium pyrophosphate (10 mM). Lysozyme treatment for permeabilizing bacterial cell walls and H₂O₂ incubation for completely quenching endogenous peroxidase of anammox sludges were essential to fluorescence enhancement and false positive signals control, respectively. Horseradish peroxidase molecules labeling at 20 °C for 12 h and the fluorescent tyramide labeling at 25 °C for 30 min with a fluorescent substrate concentration of 1:50 maintained the balance between increasing the signal and preventing nonspecific binding. Flow-CARD-FISH results showed that anammox bacteria absolute abundance in two different sludge samples were (2.31 ± 0.01) × 10⁷ and (1.20 ± 0.06) × 10⁷ cells·mL^-1, respectively, with the relative abundances of 36.7 ± 4.1% and 26.5 ± 3.7%, respectively, comparable with those of qPCR and 16S rRNA sequencing analysis. The enhanced fluorescence signals induced by CARD-FISH combined with the high quantitative fluorescence sensitivity of FCM provide a rapid and sensitive method that yields accurate quantification results that will be valuable in future studies of microbial community determination.

Recent Advances on Multi-Parameter Flow Cytometry to Characterize Antimicrobial Treatments

The investigation on antimicrobial mechanisms is a challenging and crucial issue in the fields of food or clinical microbiology, as it constitutes a prerequisite to the development of new antimicrobial processes or compounds, as well as to anticipate phenomenon of microbial resistance. Nowadays it is accepted that a cells population exposed to a stress can cause the appearance of different cell populations and in particular sub-lethally compromised cells which could be defined as viable but non-culturable (VBNC). Recent advances on flow cytometry (FCM) and especially on multi-parameter flow cytometry (MP-FCM) provide the opportunity to obtain high-speed information at real time on damage at single-cell level. This review gathers MP-FCM methodologies based on individual and simultaneous staining of microbial cells employed to investigate their physiological state following different physical and chemical antimicrobial treatments. Special attention will be paid to recent studies exploiting the possibility to corroborate MP-FCM results with additional techniques (plate counting, microscopy, spectroscopy, molecular biology techniques, membrane modeling) in order to elucidate the antimicrobial mechanism of action of a given antimicrobial treatment or compound. The combination of MP-FCM methodologies with these additional methods is namely a promising and increasingly used approach to give further insight in differences in microbial sub-population evolutions in response to antimicrobial treatments.

Assessment of total bacterial cells in extended aeration activated sludge plants using flow cytometry as a microbial monitoring tool

The extended aeration activated sludge (EAAS) process is one of the most applied biological processes in small towns. Here, we study the abundance and viability of total bacterial cells in two wastewater treatment plants (WWTPs) operating with an EAAS process. We use flow cytometry (FCM) combined with SYTO13 and propidium iodide (PI) dyes as a rapid, easy, reliable and accurate microbial monitoring tool. A disaggregation procedure with an ultrasonic bath was designed to detach total bacterial cells from activated sludge flocs for subsequent FCM analysis. This procedure permitted the recovery of total bacterial cells from sludge flocs without affecting bacterial viability, as indicated by bacterial strain controls. Since FCM is a multi-parameter technique, it was possible to determine total bacterial abundance and their viability in the activated sludge. As a comparative method, epifluorescence microscopy was also used to quantify total bacterial cells; both methods produced similar results. The FCM analysis revealed relative microbial stability in both the WWTPs. The total bacterial abundance quantified by FCM in the two plants studied was 1.02-6.23 × 10(11) cells L(-1) with 70-72% viability, one logarithm less than that reported in the literature for WWTPs using the conventional activated sludge process. This can be explained by the difference in the operational parameters between the conventional plant and EAAS, mainly the organic loading rate.

Concerning the role of cell lysis-cryptic growth in anaerobic side-stream reactors: the single-cell analysis of viable, dead and lysed bacteria

In the Anaerobic Side-Stream Reactor (ASSR), part of the return sludge undergoes alternating aerobic and anaerobic conditions with the aim of reducing sludge production. In this paper, viability, enzymatic activity, death and lysis of bacterial cells exposed to aerobic and anaerobic conditions for 16 d were investigated at single-cell level by flow cytometry, with the objective of contributing to the understanding of the mechanisms of sludge reduction in the ASSR systems. Results indicated that total and viable bacteria did not decrease during the anaerobic phase, indicating that anaerobiosis at ambient temperature does not produce a significant cell lysis. Bacteria decay and lysis occurred principally under aerobic conditions. The aerobic decay rate of total bacteria (bTB) was considered as the rate of generation of lysed bacteria. Values of bTB of 0.07-0.11 d(-1) were measured in anaerobic + aerobic sequence. The enzymatic activity was not particularly affected by the transition from anaerobiosis to aerobiosis. Large solubilisation of COD and NH4(+) was observed only under anaerobic conditions, as a consequence of hydrolysis of organic matter, but not due to cell lysis. The observations supported the proposal of two independent mechanisms contributing equally to sludge reduction: (1) under anaerobic conditions: sludge hydrolysis of non-bacterial material, (2) under aerobic conditions: bacterial cell lysis and oxidation of released biodegradable compounds.

Photobleaching with phloxine B sensitizer to reduce food matrix interference for detection of Escherichia coli serotype O157:H7 in fresh spinach by flow cytometry

A flow cytometric method (RAPID-B™) with detection sensitivity of one viable cell of Escherichia coli serotype O157:H7 in fresh spinach (Spinacia oleracea) was developed and evaluated. The major impediment to achieving this performance was mistaking autofluorescing spinach particles for tagged target cells. Following a 5 h non-selective enrichment, artificially inoculated samples were photobleached, using phloxine B as a photosensitizer. Samples were centrifuged at high speed to concentrate target cells, then gradient centrifuged to separate them from matrix debris. In external laboratory experiments, RAPID-B and the reference method both correctly detected E. coli O157:H7 at inoculations of ca. 15 cells. In a follow-up study, after 4 cell inoculations of positives and 6 h enrichment, RAPID-B correctly identified 92% of 25 samples. The RAPID-B method limit of detection (LOD) was one cell in 25 g. It proved superior to the reference method (which incorporated real time-PCR, selective enrichment, and culture plating elements) in accuracy and speed.

Role of autofluorescence in flow cytometric analysis of Escherichia coli treated with bactericidal antibiotics

Bactericidal antibiotics kill by different mechanisms as a result of a specific interaction with their cellular targets. Over the past few years, alternative explanations for cidality have been proposed based on a postulated common pathway, depending on the intracellular production of reactive oxygen species. Detection of hydroxyl radicals relies on staining with specific fluorescent dyes that can penetrate the cell and are detected using flow cytometry. Flow cytometry has become an important tool in microbiology to study characteristics of individual cells within large heterogeneous cellular populations. We show here that Escherichia coli treated with different bactericidal antibiotics exhibits increased autofluorescence when analyzed by flow cytometry. We present evidence suggesting that this change in autofluorescence is caused by altered cell morphology upon antibiotic treatment. Consistent with this view, mutant cells that fail to elongate upon norfloxacin treatment show no increased auto-fluorescence response. Finally, we present data demonstrating that changes in autofluorescence can impact the results with fluorescent probes when using flow cytometry and confound the findings obtained with specific dyes. In summary, recent findings that correlate the exposure to cidal antibiotics with the production of reactive oxygen species need to be reconsidered in light of such changes in autofluorescence. Conclusive evidence for an increase of hydroxyl radicals after treatment with such drugs is still missing.

Dual channel detection of ultra low concentration of bacteria in real time by scanning FCS

We describe a novel method to detect very low concentrations of bacteria in water. Our device consists of a portable horizontal geometry small confocal microscope with large pinhole and a holder for cylindrical cuvettes containing the sample. Two motors provide a fast rotational and slow vertical motion of the cuvette so the device looks like a simplified flow cytometer without flow. To achieve high sensitivity the design has two detection channels. Bacteria are stained by two different nucleic acid dyes and excited with two different lasers. Data are analyzed with a correlation filter based on particle passage pattern recognition. The passage of a particle through the illumination volume is compared with a Gaussian pattern in both channels. The width of the Gaussian correlates with the time of passage of the particle so one particle is counted when the algorithm finds a match with a Gaussian in both channels. The concentration of particles in the sample is deduced from the total number of coincident hits and the total volume scanned. This portable setup provides higher sensitivity, low cost and it could have a wide use ranging from clinical applications to pollution monitors and water and air quality control.

Applications of flow cytometry in plant pathology for genome size determination, detection and physiological status

Flow cytometers are probably the most multipurpose laboratory devices available. They can analyse a vast and very diverse range of cell parameters. This technique has left its mark on cancer, human immunodeficiency virus and immunology research, and is indispensable in routine clinical diagnostics. Flow cytometry (FCM) is also a well-known tool for the detection and physiological status assessment of microorganisms in drinking water, marine environments, food and fermentation processes. However, flow cytometers are seldom used in plant pathology, despite FCM's major advantages as both a detection method and a research tool. Potential uses of FCM include the characterization of genome sizes of fungal and oomycete populations, multiplexed pathogen detection and the monitoring of the viability, culturability and gene expression of plant pathogens, and many others. This review provides an overview of the history, advantages and disadvantages of FCM, and focuses on the current applications and future possibilities of FCM in plant pathology.

A microfluidic device for bacteria detection in aqueous samples

We demonstrate the use of a microfluidic device that accurately monitors bacteria levels in water. Fluorescent antibody labelled E. coli K12 bacteria in aqueous samples are flowed through the device, and spikes in the emission signal correspond to the presence of bacteria. Target bacteria could also be detected while suspended in a suspension of very low antibody concentration, suggesting that washing of bacteria could be avoided to make the detection automated and more rapid. Use of a microfluidic device will eventually enable quick on-site detection of bacteria using small quantities of sample.

Flow cytometry: an introduction

A flow cytometer is an instrument that illuminates cells (or other particles) as they flow individually in front of a light source and then detects and correlates the signals from those cells that result from the illumination. In this chapter, each of the aspects of that definition will be described: the characteristics of cells suitable for flow cytometry, methods to illuminate cells, the use of fluidics to guide the cells individually past the illuminating beam, the types of signals emitted by the cells and the detection of those signals, the conversion of light signals to digital data, and the use of computers to correlate and analyze the data after they are stored in a data file. The final section of the chapter will discuss the use of a flow cytometer to sort cells. This chapter can be read as a brief, self-contained survey. It can also be read as a gateway with signposts into the field. Other chapters in this book will provide more details, more references, and even an intriguing view of the future of cytometry.

Bacteria permeabilization and disruption caused by sludge reduction technologies evaluated by flow cytometry

Technologies proposed in the last decades for the reduction of the sludge production in wastewater treatment plants and based on the mechanism of cell lysis-cryptic growth (physical, mechanical, thermal, chemical, oxidative treatments) have been widely investigated at lab-, pilot- and, in some cases, at full-scale but the effects on cellular lysis have not always been demonstrated in depth. The research presented in this paper aims to investigate how these sludge reduction technologies affect the integrity and permeabilization of bacterial cells in sludge using flow cytometry (FCM), which permits the rapid and statistically accurate quantification of intact, permeabilised or disrupted bacteria in the sludge using a double fluorescent DNA-staining instead of using conventional methods like plate counts and microscope. Physical/mechanical treatments (ultrasonication and high pressure homogenisation) caused moderate effects on cell integrity and caused significant cell disruption only at high specific energy levels. Conversely, thermal treatment caused significant damage of bacterial membranes even at moderate temperatures (45-55 °C). Ozonation significantly affected cell integrity, even at low ozone dosages, below 10 mgO(3)/gTSS, causing an increase of permeabilised and disrupted cells. At higher ozone dosages the compounds solubilised after cell lysis act as scavengers in the competition between soluble compounds and (particulate) bacterial cells. An original aspect of this paper, not yet reported in the literature, is the comparison of the effects of these sludge reduction technologies on bacterial cell integrity and permeabilization by converting pressure, temperature and ozone dosage to an equivalent value of specific energy. Among these technologies, comparison of the applied specific energy demonstrates that achieving the complete disruption of bacterial cells is not always economically advantageous because excessive energy levels may be required.

Development of a density slicer for the simple collection of respective density layers after stepwise density gradient centrifugation

Density gradient centrifugation (DGC) is useful for the separation of living microbial cells from food samples that are not filterable. After DGC, however, careful operation is necessary to collect each density layer. For a simple and reproducible collection after DGC, we have developed a seamless operation system composed of a 5-needle unit, a microchannel plate, and a microflow controller, and named this a density slicer system. Two types of 5-needle units were devised and both showed nearly the same performance. Reproducible results with the automatic operation system could be demonstrated using an Escherichia coli cell suspension.

Direct quantification of bacterial biomass in influent, effluent and activated sludge of wastewater treatment plants by using flow cytometry

A rapid multi-step procedure, potentially amenable to automation, was proposed for quantifying viable and active bacterial cells, estimating their biovolume using flow cytometry (FCM) and to calculate their biomass within the main stages of a wastewater treatment plant: raw wastewater, settled wastewater, activated sludge and effluent. Fluorescent staining of bacteria using SYBR-Green I + Propidium Iodide (to discriminate cell integrity or permeabilisation) and BCECF-AM (to identify enzymatic activity) was applied to count bacterial cells by FCM. A recently developed specific procedure was applied to convert Forward Angle Light Scatter measured by FCM into the corresponding bacterial biovolume. This conversion permits the calculation of the viable and active bacterial biomass in wastewater, activated sludge and effluent, expressed as Volatile Suspended Solids (VSS) or particulate Chemical Oxygen Demand (COD). Viable bacterial biomass represented only a small part of particulate COD in raw wastewater (4.8 +/- 2.4%), settled wastewater (10.7 +/- 3.1%), activated sludge (11.1 +/- 2.1%) and effluent (3.2 +/- 2.2%). Active bacterial biomass counted for a percentage of 30-47% of the viable bacterial biomass within the stages of the wastewater treatment plant.

Detection of Clostridium tyrobutyricum spores using polyclonal antibodies and flow cytometry

AIMS

The present work investigates the feasibility of using flow cytometry (FCM) combined with fluorescent-labelled specific polyclonal antibodies for the detection and presumptive identification of Clostridium tyrobutyricum spores in bovine milk.

METHODS AND RESULTS

Two fluorescent molecules (fluorescein isothiocyanate and Alexa Fluor 488) were conjugated to antispores polyclonal antibodies. Side scatter and forward scatter profiles of the Cl. tyrobutyricum spores marked with fluorescent antibodies permitted the detection of spores and differentiated them from other related microbial species. The detection limit of this method was 10(3) spores per 100 ml of milk, and results could be achieved in 2 h.

CONCLUSIONS

FCM combined with fluorochrome-conjugated antibodies, especially Alexa Fluor, could be an efficacious means to detect and provide presumptive identification of Cl. tyrobutyricum spores, as well as differentiation from other Clostridium species that can also cause late blowing in cheese.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study describes the basis for the development of a method suitable for analysis of milk destined for cheese manufacture that would permit the detection of Cl. tyrobutyricum spores in a short period. This would enable the industry to use contaminated milk for dairy products other than cheese where Cl. tyrobutyricum does not cause a problem.

Separation of viable histamine-producing bacteria from yellowtail meat components by density gradient centrifugation

Quantitative separation of live cells from food samples is essential for non-culture methods to be validated. In this viewpoint, the feasibility of density gradient centrifugation (DGC) was demonstrated for the first time using samples of yellowtail meat to which Morganella morganii, a histamine producing bacterium had been added. Using a Ficoll density gradient from 50 to 10 w/v % with 10 w/v % steps, meat-free fractions of M. morganii cells were collected in 20-50 w/v % layers. The total cell collection rate ranged from 73-86 % irrespective of the cell density in the range 10(2)-10(6) cells/200 microl.

Considering the first steps toward a stable and orderly way of bacterial life

The development of a short-time scale colloidal system introduces flow cytometry as a tool to investigate both physicochemical and molecular aspects of bacterial adhesion to solid surfaces.

Rapid methods for diagnosis of bloodstream infections

Direct detection technologies for pathogenic microorganisms are emerging to be applied in the diagnosis of serious bloodstream infections and infections at sterile body sites, as well as for quality control measures prior to the release of sterile blood products and to ascertain microbial safety of food. Standard blood cultures as the current gold standard for detection of bacteraemia/sepsis and other culture-based microbiological identification procedures are comparatively slow and have limited sensitivity for fastidious or slow-growing microorganisms. Rapid nucleic acid-based technologies with PCR amplification or hybridisation probes for specific pathogens, broad-range bacterial or fungal assays, flow cytometry, as well as protein-based characterisation by mass spectrometry, aim at identification of pathogenic microorganisms within minutes to hours. Interpretation of direct detection of panbacterial or panfungal nucleic acids instead of living microorganisms in blood is complex, given the risk of contamination, the ubiquitous presence of bacterial and fungal DNA, and the lack of a gold standard. Since many of the infections at sterile sites, particularly sepsis, are medical emergencies requiring immediate therapeutic responses, rapid technologies could contribute to reduction of morbidity, mortality, and of the economic burden. This review summarises the currently available data on rapid non-culture-based technologies and outlines the potential clinical usefulness in infectious disease diagnosis.

A short-time scale colloidal system reveals early bacterial adhesion dynamics

The development of bacteria on abiotic surfaces has important public health and sanitary consequences. However, despite several decades of study of bacterial adhesion to inert surfaces, the biophysical mechanisms governing this process remain poorly understood, due, in particular, to the lack of methodologies covering the appropriate time scale. Using micrometric colloidal surface particles and flow cytometry analysis, we developed a rapid multiparametric approach to studying early events in adhesion of the bacterium Escherichia coli. This approach simultaneously describes the kinetics and amplitude of early steps in adhesion, changes in physicochemical surface properties within the first few seconds of adhesion, and the self-association state of attached and free-floating cells. Examination of the role of three well-characterized E. coli surface adhesion factors upon attachment to colloidal surfaces—curli fimbriae, F-conjugative pilus, and Ag43 adhesin—showed clear-cut differences in the very initial phases of surface colonization for cell-bearing surface structures, all known to promote biofilm development. Our multiparametric analysis revealed a correlation in the adhesion phase with cell-to-cell aggregation properties and demonstrated that this phenomenon amplified surface colonization once initial cell-surface attachment was achieved. Monitoring of real-time physico-chemical particle surface properties showed that surface-active molecules of bacterial origin quickly modified surface properties, providing new insight into the intricate relations connecting abiotic surface physicochemical properties and bacterial adhesion. Hence, the biophysical analytical method described here provides a new and relevant approach to quantitatively and kinetically investigating bacterial adhesion and biofilm development.

When bacteria grow on solid surfaces, they can form three-dimensional communities called biofilms. Within these complex structures, bacteria can develop specific tolerance to different microbiocides, causing serious health and economic problems. Investigations of the key molecular events involved in biofilm formation have shown that surface-exposed adhesin proteins promote this process, but many questions remain regarding the mechanisms and biophysics of surface adhesion. We introduced an original approach to investigating the very early steps in bacterial adhesion that uses dispersed colloidal surfaces as microbial adhesion substrates. Using flow cytometry, we performed a quantitative real-time analysis of adhesion kinetics of several strains of the bacterium Escherichia coli, which were genetically engineered to produce well-characterized cell-surface adhesins that are known to promote biofilm development. We provide evidence for previously unknown adhesin-dependent behaviors, such as clear-cut differences in the very initial phases of surface colonization. We also demonstrate that initial adhesion correlates with almost instant surface property changes, and that cell-to-cell association might serve as an amplification mechanism for surface colonization. We therefore provide a new understanding of the intricate relationships between the physico-chemistry of abiotic surfaces and bacterial adhesion.

Combining micrometric colloidal beads as adhesion substrates with flow cytometric analysis allows for a high-resolution analysis that reveals adhesin-dependent behavior in the very first steps of surface colonization by bacteria.

Flow cytometric quantification of bacteria in vaginal swab samples self-collected by adolescents attending a gynecology clinic

Bacterial vaginosis (BV) is an important risk factor in reproductive health outcomes, such as pre-term birth and sexually transmitted infections including HIV. However, its etiology, diagnosis and treatment remain poorly defined. We evaluated flow cytometry as a tool to quantify total bacterial cells in vaginal specimens self-collected longitudinally by adolescents. BV was diagnosed by Gram-stain (criteria of Hay and Ison). Average flow cytometric counts of bacterial cell-units (BCU) was log(10) 8.04 per gram sample and was found to correlate with sample weight (p<0.0001). BV was frequently observed in this group, with 22 of 32 participants (69%) diagnosed with BV for at least one timepoint. Surprisingly, increased BCU was associated with normal Hay-Ison score (p=0.0003), even when adjusting for sample weight (p=0.02). Since presence and quantity of Lactobacillus defines normal vaginal microbiology (ie. absence of BV), this result indicates a possible bias towards dominance of Lactobacillus cells in measurements of "total" BCU. Increased BCU per gram was associated in multivariate analysis with longer self-reported time since last menstruation (p=0.004) and last sexual intercourse (p=0.007). Sperm was detected in 3 samples provided by those reporting sexual intercourse in the previous 24 h. Light-scattering profiles of bacteria and vaginal cells in samples collected over time from an individual were often identical and distinct from other individuals. To our knowledge, this is the first description of flow cytometry for analysis of commensal bacteria in vaginal specimens. Further development may help to illuminate the complex dynamics of vaginal microbial communities underlying BV.

Enrichment of Yersinia pestis from blood cultures enables rapid antimicrobial susceptibility determination by flow cytometry

Mortality from plague is high if not treated with the proper antibiotics within 18-24 hours after onset of symptoms. The process of antibiotic susceptibility determination of Yersinia pestis isolated from blood samples may extend from 4 to more than 7 days, since the in vitro growth is very slow. To accelerate this process, we developed an enrichment protocol as well as a non-standard yet reliable method for rapid antibiotic susceptibility analysis of Y. pestis from blood cultures using flow cytometry technology. This rapid method is applicable to blood cultures containing low levels of Y. pestis.

Modes of cytometric bacterial DNA pattern: a tool for pursuing growth

Analyses of DNA pattern provide an excellent tool to determine activity states of bacteria. Bacterial cell cycle behaviour is generally different from the eukaryotic one and is pre-determined by the bacteria's diversity within the phylogenetic tree, and their metabolic traits. As a result, every species creates its specific proliferation pattern that differs from every other one. Up to now, just few bacterial species have been investigated and little information is available concerning DNA cycling even in already known species. This prevents understanding of the complexity and diversity of ongoing bacterial interactions in many ecosystems or in biotechnology. Flow cytometry is the only possible technique to shed light on the dynamics of bacterial communities and DNA patterns will help to unlock the hidden principles of their life. This review provides basic knowledge about the molecular background of bacterial cell cycling, discusses modes of cell cycle phases and presents techniques to both obtain DNA patterns and to combine the contained information with physiological cell states.

Hydrodynamic focusing investigation in a micro-flow cytometer

Hydrodynamic focusing behavior is characterized by two fluids coflowing at different velocities inside a micro-flow cytometer. In this study, a two-fluid model has been established to describe the flow transport behavior and interaction of sample and sheath fluids. The analysis treats the sample and sheath fluids as two-dimensional, laminar, incompressible, and isothermal. The theoretical model comprises two groups of transient conservation equations of mass and momentum with consideration of the interfacial momentum exchange. The governing equations are solved numerically through an iterative SIMPLEC algorithm to determine the flow properties. Since the ratio of the sheath velocity to the sample velocity varies from 5 to 70, the predicted focusing width and length are in good agreement with the experimental data in the literature. In addition, the present study explored the hydrodynamic focusing flowfield as well as the pressure drop across a micro-flow cytometer and the time needed for the completion of one focusing event in detail. To enhance the understanding of hydrodynamic focusing in the design of cytometers, ten numerical experiments were conducted to examine the effects of the inner nozzle length, inner nozzle exit width, inner nozzle shape, and fluid properties on the width of the focused sample stream.

Rapid identification ofHelicobacter pylori by capillary electrophoresis: an overview

Helicobacter pylori can cause gastritis and peptic ulcers and is directly associated with the development of gastric cancer. There are many types of diagnostic methods used to identification H. pylori (invasive and non-invasive), but these methods usually require time-consuming and laborious procedures and therefore are not capable of fast diagnosis in cases of emergency. This contribution describes the new achievements, interdisciplinary significance and some future directions in the application of capillary electrophoresis for determination of H. pylori.

Rapid identification ofEscherichia coli andHelicobacter pylori in biological samples by capillary zone electrophoresis

The differences in surface charge of different bacteria can be exploited for their separation by capillary electrophoresis. However, this method of separation of microorganisms is beset with various drawbacks such as adhesion of bacteria to the fused silica surface or cluster formation. To overcome these phenomena we investigated the addition of poly(ethylene oxide) as a focusing agent to the running buffer and used calcium and myoinositol hexakisphosphate as specific ions that interact with the bacterial surface, changing its electrical properties and electrophoretic mobilities. In the present work, we applied CZE to identification of E. coli in infected urine (direct injection) from patients with urinary tract infections and to identification of Helicobacter pylori, which is a gram-negative bacillus responsible for one of the most common infections found in humans worldwide. Helicobacter pylori colonize the stomach and are responsible for severe diseases of the gastric tract, ranging from chronic gastric ulcer to gastric cancer.

Microbial biomass estimation

The development of a fully automated on-line monitoring and control system is very important in bioprocesses. One of the most important parameters in these processes is biomass. This review discusses different methods for biomass quantification. A general definition of biomass and biovolume are presented. Interesting concepts about active but not culturable cells considerations are included as well as concepts that must be taken into account when selecting biomass quantification technology. Chemical methods have had few applications in biomass measurement to date; however, bioluminescence can selectively enumerate viable cells. Photometric methods including fluorescence and scattered light measurements are presented. Reference methods including dry and wet weight, viable counts and direct counts are discussed, as well as the physical methods of flow cytometry, impedancimetric and dielectric techniques.

Flow-cytometric detection of changes in the physiological state of E. coli expressing a heterologous membrane protein during carbon-limited fedbatch cultivation

The key to optimizing productivity during industrial fermentations is the ability to rapidly monitor and interpret the physiological state of single microbial cells in a population and to recognize and characterize different sub-populations. Here, a flow cytometry-based method for the reproducible detection of changes in membrane function and/or structure of recombinant E. coli JM101 (pSPZ3) expressing xylene monooxygenase (XMO), was developed. XMO expression led to compromised but not permeabilized cell membranes. This was deduced from the fact that recombinant cells only stained with ethidium bromide (EB) and not with propidium iodide (PI). During the glucose-limited fedbatch cultivation, an increase from 25% to 95% of EB-stained cells was observed, occurring between 2 and 5 h after induction. Control experiments confirmed that this increase was due to the recombinant protein production and not caused by any possible effects of varying substrate availability, high cell density, plasmid replication or the presence of the inducing agent. We hypothesize that the integration of the recombinant protein into the cell membrane physically disrupted the functionality of the efflux pumps, thus resulting in EB-staining of the recombinant cells. This method enabled us to detect changes in the physiological state of single cells 2-4 h before other indications of partial cell damage, such as unbalanced growth, acetate accumulation and an increased CO(2) production rate, were observed. This method therefore shows promise with respect to the further development of an early-warning system to prevent sudden productivity decreases in processes with recombinant E. coli expressing heterologous membrane proteins.

A rapid method combining immunofluorescence and flow cytometry for improved understanding of competitive interactions between lactic acid bacteria (LAB) and methicillin-resistant S. aureus (MRSA) in mixed culture

The increasing frequency of methicillin-resistant Staphylococcus aureus (MRSA) infections in hospital and community settings highlights the need for effective anti-MRSA agents that will not contribute to the growing problem of antibiotic resistance. Lactic acid bacteria (LAB) are known to exclude various pathogens through multiple mechanisms. In vitro models studying interactions of pathogens and LAB in mixed cultures use selective agar plates to quantify changes in target populations. We applied commercially available S. aureus-specific polyclonal antibodies conjugated with fluorescein isothiocyanate (FITC) for this purpose, producing a bright green signal that clearly differentiates S. aureus from LAB species when mixed cultures are analyzed by flow cytometry and fluorescent microscopy. Flow cytometry of mixed cultures revealed a much larger population of MRSA cells than was detectable using selective agar plates. To our knowledge, this is the first time immunofluorescent flow cytometry has been applied to the study of competitive exclusion in mixed bacterial populations over time.

Separation of microorganisms using electromigration techniques

Like other colloidal particles bacteria have a surface charge that originates from the ionization of surface molecules and of the adsorption of ions from solution. Bacterial cell wall and membranes containing numerous proteins, lipid molecules, teichoic acids, lipopolisaccharides which give them characteristic charge. Therefore, bacterial cells undergo electrophoresis in a free solution with their own mobility depending on ionic strength and pH of buffer solution. Various electromigration techniques can be used to separate and determine the intact cells. Successful separation of five species of bacteria was obtained using a trimethylchlorosilane-modified capillary and a divinylbenzene-modified with suppressed EOF over a short distance (8.5 cm). The utilization of coated capillaries prevents adsorption of bacteria to the capillary wall. Another approach is utilization of a dilute dissolved polymer, polyethylene oxide (PEO) in the running buffer as a non-bonded coating for the purpose of altering the EOE These experiment have proved the possibility of diagnosing a variety of diseases and the ability to separate and identify viable cells.

Flow-cytometric cell sorting and subsequent molecular analyses for culture-independent identification of bacterioplankton involved in dimethylsulfoniopropionate transformations

Marine bacterioplankton transform dimethylsulfoniopropionate (DMSP) into the biogeochemically important and climatically active gas dimethylsulfide. In order to identify specific bacterial taxa mediating DMSP processing in a natural marine ecosystem, we amended water samples from a southeastern U.S. salt marsh with 20 microM DMSP and tracked community shifts with flow cytometry (FCM) coupled to 16S rRNA gene analyses. In two out of four seasons studied, DMSP amendments induced the formation of distinct bacterioplankton populations with elevated nucleic acid (NA) content within 24 h, indicative of cells actively utilizing DMSP. The 16S rRNA genes of the cells with and without elevated NA content were analyzed following cell sorting and PCR amplification with sequencing and terminal restriction fragment length polymorphism approaches. Compared to cells in the control FCM populations, bacteria with elevated NA content in the presence of DMSP were relatively enriched in taxa related to Loktanella, Oceanicola, and Sulfitobacter (Roseobacter lineage, alpha-Proteobacteria); Caulobacter (alpha-Proteobacteria); and Brachymonas and Xenophilus (beta-Proteobacteria) in the May-02 sample and to Ketogulonicigenium (Roseobacter lineage, alpha-Proteobacteria) and novel gamma-Proteobacteria in the Sept-02 sample. Our study suggests that diverse bacterioplankton participate in the metabolism of DMSP in coastal marine systems and that their relative importance varies temporally.

Rains, drains and active strains: towards online assessment of wastewater bacterial communities

Wastewater treatment is one of the largest scale and arguably the most commercially important biotechnological process in the world. Bacterial breakdown of waste materials facilitates the safe disposal of effluents into receiving water bodies. Given this significance, research has focused on identifying the keystone species on which efficient treatment is based. However, unravelling the microbial diversity within such systems has proven difficult. This is highlighted by our lack of detailed knowledge of the microbial interactions within these complex populations, limiting our ability to fully exploit bacterial degradative abilities. Even with the incorporation of new emerging molecular techniques, there have been no investigations linking genetic sequence to microbial function and successful treatment operation. To reach this goal, researchers need the ability to identify, enumerate and monitor the metabolic functions of subpopulations within these complex bacterial communities. Flow cytometry (FCM) combined with fluorescence-based molecular identification techniques provides a method for such studies. Moreover, single-cell sorting provides a unique opportunity to identify and remove individual cells of interest. Laboratory culture of sorted cells is often possible and permits the use of more traditional microbiological techniques to backup molecular investigations. Utilising this approach will advance our understanding of wastewater treatment processes and help maintain and enhance plant operation to improve efficiency.

Analysis of the microbial functional diversity within water-stressed soil communities by flow cytometric analysis and CTC+ cell sorting

Total and active cell counts within soil samples were determined by culture-independent methods using flow cytometry and preparative Nycodenz gradient centrifugation. Whole cells were purified from soil cores and total extractable cell counts assessed by SYBR Green II fluorescence, while active cell counts were determined by 5-cyano-2,3-ditolyl tetrazolium chloride reduction (CTC+ cells). Parallel microcosms, maintained at either field water capacity or subjected to drying, indicated that the total extractable cell count remained between 10(8) and 10(9) g(-1) (dry weight). In contrast, the CTC+ active count fell threefold in dried microcosms (6% of total cell count) when compared to wetted microcosms (18% of total cell count). Specifically, these data highlighted an overall deactivation of microbial biomass during water stress, with 16S rDNA analyses of flow-sorted CTC+ cells demonstrating shifts within the active diversity. Flow cytometry coupled with cell purification techniques represents a significant tool for operationally defining an active and redundant microbial component within soil communities and is demonstrated during water stress.